Finally, HHLA2 expression in cancer tissue (p = 0.049; HR = 0.156; 95% CI = 0.025–0.992) and sensitivity to platinum chemotherapy (p = 0.002; HR = 14.14; 95% CI = 2.632–75.916) were identified as independent factors influencing the patient prognosis (Fig. 3d, e), and HHLA2 was an indicator of a better prognosis for ovarian cancer. The gene discussed is HHLA2; the disease is ovarian cancer.